Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased. Currently, research into lithium secondary batteries, as batteries that may best satisfy the above need, has actively conducted.
In general, an electrode density or electrode porosity of electrodes used in a lithium secondary battery is obtained in a state in which a slurry is prepared by mixing a cathode or anode active material with a solvent, if necessary, a binder and a conductive agent and stirring, an electrode base material of a cathode or anode formed of a metallic material is coated therewith and dried, and the dried electrode based material is then pressed at an appropriate pressure. In this case, the electrode density is increased while the porosity decreases as the applied pressure increases.
In the lithium secondary battery, the electrode density and electrode porosity may be related to various battery characteristics including energy density of the battery, electrical conductivity of the electrode, and ionic conductivity. Thus, appropriate electrode density and electrode porosity may be different from desired battery characteristics, and it is very important to minimize the deviation thereof in a production process of the electrode.
To date, a method of measuring an electrode density (D) is performed in such a manner that weight and thickness of an electrode are measured by sampling a specific area of the electrode when needed, and the density is measured using a value in which mass and thickness of an electrode base material, i.e., a metal such as copper or aluminum, having the same area are subtracted from the respective measured values.
Also, the electrode density obtained by sampling the specific area of the electrode is subtracted from 1 to obtain a value, and an electrode porosity (P) is obtained by dividing the value by the density of the electrode excluding the electrode base material and then calculating in terms of percentage.
The measurements of the electrode density and the electrode porosity by the above methods may have the following limitations. First, since an electrode must be sampled whenever density and porosity of each electrode are needed, a portion of the electrode must be destructed for each measurement. Thus, it may be time consuming as well as cost consuming. Also, since an electrode base material must be dissolved in a predetermined solvent to measure the density and thickness of the electrode excluding the electrode base material, a measurement process may be complicated.
Therefore, there is a need to provide a method of efficiently measuring electrode density and electrode porosity while not destructing an electrode to be measured and reducing errors.